1. Field of the Invention
The present invention is a retractable USB memory stick and more particularly, to such a retractable USB memory stick provided with a safety hook that can be opened or closed.
2. Description of the Related Art
USB memory stick is a mobile data storage device connectable to a computer for data access and convenient for carrying. Following fast development of technology, the storage capacity and application range of USB memory stick have been greatly improved. For example, 1G, 4G, 8G, 16G as well as 32G USB memory sticks are commercially available.
A retractable USB memory stick is known comprising a PC board having a USB interface circuit and a memory IC package, an insulative PC board holder holding the PC board, and a housing formed of two insulative half shells for accommodating the insulative PC board holder. The insulative PC board holder has a push member extended out of the housing and operable to move the USB interface circuit in and out of the housing.
Taiwan Patent Utility Model M377749 discloses a retractable USB memory stick with a hook, which is an invention of the present inventor. According to this design, the retractable USB memory stick comprises a metal casing, a PC board and an insulation PC board holder. The PC board is detachably accommodated in a recess in the insulation PC board holder. The insulation PC board holder comprises a base portion, a hook located on the rear side of the base portion, a front extension located on the front side of the base portion, a sliding block supported on a bridged spring strip at the base portion. The metal casing has a sliding slot, which receives the sliding block of the insulation PC board holder to guide sliding movement of the insulation PC board holder relative to the metal casing, and multiple positioning holes located on the sliding slot at different locations. The sliding block of the insulation PC board holder is selectively forced into friction engagement with one of the positioning holes. By means of the hook, the retractable USB memory stick can be fastened to a chain. This design facilitates replacement of the metal casing and the PC board.
When the sliding block is positioned in the first positioning hole of the metal casing, the front extension of the insulation PC board holder is extended out of the front opening of the metal casing. When the sliding block is positioned in the second positioning hole of the metal casing, the hook of the insulation PC board holder is extended out of the rear opening of the metal casing and the access gap is kept inside the metal casing. When the sliding block is positioned in the third positioning hole of the metal casing, the front extension and base portion of the insulation PC board holder are received inside the metal casing, the hook of the insulation PC board holder is extended out of the rear opening of the metal casing and the access gap is disposed outside the metal casing. Based on the aforesaid arrangement, the retractable USB memory stick can be fastened to a chain by the hook.
According to the aforesaid retractable USB memory stick, the hook is located on the rear side of the insulation PC board holder and defines an access gap, and the metal casing provides three positioning holes for the positioning of the sliding block selectively. The design of the three positioning holes complicates the fabrication of the metal casing and the operation of the retractable USB memory stick. The access gap will be kept inside the metal casing when the sliding block is positioned in the second positioning hole of the metal casing. However, the sliding block may be forced away from the second positioning hole to the third positioning hole accidentally upon an impact, causing the access gap to be exposed to the outside of the metal casing. When this condition occurs, the hook may fall from the chain. Therefore, an improvement in this regard is necessary.